Abstract

Dendritic spines are small protrusions from dendrites that host the majority of excitatory synapses in the central nervous
system. Structurally, excitatory synapses located on dendritic spines are asymmetric, with a presynaptic bouton that contains
round clear vesicles apposed to a postsynaptic density where glutamate receptors are anchored. Spines form biochemical compartments
that can isolate activated signalling pathways that occur at one synapse from those at other synapses, thereby providing a
way to enhance the specificity of connections between neurons in the brain. Structural changes of dendritic spines in response
to stimulation facilitate changes in synaptic strength, and these changes are likely to underlie important higher brain functions
such as learning and memory. Dysregulation of spine morphology is seen in several neurological disorders such as Alzheimer's
disease and fragile X syndrome.

Key Concepts

Spines are the primary site of excitatory synapses.

Smooth endoplasmic reticulum can form complex structures localized to large spines.

The cytoskeleton of spines is mostly composed of actin.

Trans‐synaptic adhesion molecules as well as proteins secreted from astroglia help stabilise synapses.

Figure 4. (a) Long‐term potentiation (LTP) demonstrated by enhanced synaptic response following a brief, high‐frequency stimulation (arrow) in the stratum radiatum of CA1 in the hippocampus. (b) Hippocampal slice preparation with stimulating electrode activating CA3 Schaeffer collaterals and recording electrode in the stratum radiatum of CA1. (c) LTP in the adult results in larger spines. Total synaptic area is balanced by a loss in small spines. (d) LTP in young animals (P15) results in an increase in spine density and an overall increase in synaptic area. (e) Nascent zones (blue) are decreased initially after induction of LTP (30 min) but at 2 h are increased.